The Grand Canyon became a fully protected US National Park in 1919. The Perth Canyon, off the coast of Fremantle, has barely been heard of, though at 1.5 kilometres deep, it rivals its famous Arizonan cousin.

You can't visit the Perth Canyon in a campervan, but it is extremely popular with recreational fishermen. It is also popular with pygmy blue whales, which is why the Environment Minister, Tony Burke, proudly named it this week a key area to be covered by Australia's massive new network of marine reserves.

Once Burke's carefully drawn-up plan becomes law, fishing will be banned over parts of the Perth Canyon, infuriating the recreational fishing industry, which says that as many as 600,000 people - one third of the Western Australian population - enjoy throwing a line over the side.

In doing this, the Gillard government is opening yet another front in its various battles with primary producers. The government has fought cattle farmers over live exports and irrigators over the Murray-Darling Basin. On the broad environment front, it's fighting several industries on the carbon tax. Now it's in a blue with fishermen.

The industry's case is that it already fishes sustainably. In fact Australia has some of the best fisheries management in the world. If the government wants to protect our oceans, it should look elsewhere - port development, shipping, pollution, sediment run-off, climate change. Overfishing is not the culprit.

''They seem to be proud of the fact that they're cauterising an important part of our economic activity and a major export industry,'' says Guy Leyland, spokesman for the Western Australian Fishing Industry Council. ''Our fisheries are very well managed, so what's the purpose of this? It's certainly not to protect fish from overfishing because we don't overfish.

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''You feel you're in some sort of parallel universe where productive activities are frowned upon and should be shut down.''

The upshot, he says, would be that imports, which already make up 70 per cent of the seafood Australians eat, would get a free kick, while the price of domestic produce would rise.

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Recreational fishermen are equally bewildered, saying their activities have no impact on the Perth Canyon. Andrew Rowland, the chief executive of Recfishwest, blamed a ''green agenda''. It's a view echoed around the industry.

''The conservation values of that particular water focused around blue whales, and we believe recreational fishing posed absolutely no threat to blue whales. Unfortunately politics has got in the way of science and logic,'' he said.

Jessica Meeuwig, a professor at the University of Western Australia's oceans institute, had two words for that.

''That's bullshit,'' she said. ''They're using deepwater power winches and deepwater lines to pull up large species like hapuku from the depths.''

Physical features like the canyon are magnets to marine life, she explained. Fishing in such areas is like shooting fish in a barrel.

''Protecting the Perth Canyon is actually about saying, 'This is a key feature. We need to understand what intact marine ecosystems look like.'''

The Pew Environment Group's Imogen Zethoven - the main campaigner on the Coral Sea, which is the most prominent area receiving protection - says the best comparison is with national parks on land.

''You've got a magnificent forest, that is pristine, home to all these species of animals, and you can walk through it and marvel at it in its natural state. And then someone claims you can log it sustainably.

''That's what this is about. It's not about whether fishing is sustainable or not, it's about areas that are very precious, very beautiful and very important.''

Leyland says the industry has no problem with setting aside areas for complete conservation. They know the public wants that.

''It's just the extent of it,'' he says.

About 12 per cent of Australia's land is under some form of conservation protection, whether national or state parks, nature parks or conservation reserves. The highest level of marine protection - ''no take'' fishing areas, which are roughly comparable to land protection areas, the recent NSW government hunting decision aside - accounts for about 13 per cent with this week's additions.

This week's announcement is a big moment for the Environment Minister, who along with the Prime Minister, Julia Gillard, will probably be the toast of next week's Rio+20 sustainability conference.

One matter for which nobody faults Burke is his patient consultation. Everybody with a view got a hearing, usually several. But, after all the talk, fishermen are convinced they got the raw prawn.

''I've been trawling for 40 years,'' says the Queensland Seafood Industry Association president, Geoff Tilton. ''I don't want to catch turtles and I've done everything possible to make sure I only catch what I'm chasing, which is prawns. We'll just end up importing more prawns from countries that have lower standards than us.''

Nor are they persuaded by the $100 million figure the government has floated as a financial assistance package. An earlier package for Great Barrier Reef Marine Park has cost nearly $250 million, they say.